Enhance Nullable Union Type Inference through Strict Mode

[antoniel]

Summary

This PR addresses issue #1474, aiming to improve the type inference mechanism for nullable union types in tsoa. By enabling TypeScript's strict mode, we significantly enhance the accuracy of type definitions and OpenAPI Schemas generated by the library.

Changes

• Modified TypeScript program's compilerOptions to include strict: true.
• Adjusted relevant unit tests to validate the improved type inference.

Impact

• This change may modify the output of existing API definitions. However, it enhances the schema's accuracy without limiting the current scope.

How to Test

1. Pull the changes and install updated dependencies.
2. Run the existing unit tests to validate that the change is working as expected.
3. Manually create a route using a nullable union type and confirm that the generated OpenAPI schema is accurate.

Context

• Library Version: 5.1.1
• Node Version: 18.12.0
• Package Manager: Yarn

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[WoH]

Does setting it in the tsconfig of your tsoa's config file not work? See https://github.com/lukeautry/tsoa/blob/master/packages/runtime/src/config.ts#L41C14-L41C14

I am worried this might have unintended consequences when we run this on strict: false codebases and break typing completely. That said, maybe strict: true is by now common enough to test it.

[antoniel]

Thank you for your suggestion! I did try setting it in the tsoa's config file, and it seems to work well. I agree that ensuring compatibility is essential. However, in scenarios where the OpenAPI file serves as a blueprint to generate validation schemas using tools like Zod, maintaining accurate type representation is critical. Having just string instead of string | null could lead to serious issues.

[antoniel]

Maybe we can add explicitly in the documentation that setting the tsoa as strict in their config files is highly recommended, even if the tsconfig is not strict.

[WoH]

That would be highly appreciated.